A258767 With a(1) = 1, a(n) is the smallest number not already in the sequence such that a(n)^2 + a(n-1)^2 is not squarefree.

1, 7, 14, 2, 4, 3, 6, 8, 10, 5, 12, 9, 13, 16, 18, 15, 20, 21, 22, 11, 23, 36, 24, 26, 28, 29, 47, 46, 30, 25, 35, 40, 32, 34, 17, 19, 33, 27, 31, 42, 38, 41, 37, 39, 45, 48, 44, 50, 49, 43, 51, 54, 52, 56, 58, 59, 62, 60, 55, 65, 70, 63, 57, 66, 64, 68, 72, 69, 67, 81, 75, 78, 71, 53, 79, 97, 96, 74

Offset

1,2

Comments

Believed to be a permutation of the natural numbers.

Links

Reinhard Zumkeller, Table of n, a(n) for n = 1..10000

Prog

(PARI) v=[1]; n=1; while(n<100, if(!issquarefree(n^2+v[#v]^2)&&!vecsearch(vecsort(v), n), v=concat(v, n); n=0); n++); v
(Haskell)
import Data.List (delete)
a258767 n = a258767_list !! (n-1)
a258767_list = 1 : f 1 [2..] where
   f x zs = g zs where
     g (y:ys) | a008966 (x^2 + y^2) == 1 = g ys
              | otherwise = y : f y (delete y zs)
-- Reinhard Zumkeller, Jun 11 2015

Crossrefs

Cf. A256271, A075380.

Cf. A258768 (fixed points).

Cf. A008966, A258827 (putative inverse).

Sequence in context: A227173 A178998 A188929 * A169845 A302972 A115146

Adjacent sequences: A258764 A258765 A258766 * A258768 A258769 A258770

Keyword

nonn

Author

Derek Orr, Jun 09 2015

Status

approved